The job of the author wasn't to build the feature in the X weeks, it was to manage the customer while the project completed in whatever time it took. He was successful too, even though he doesn't seem to realise that was his primary value-add.
The customer didn't want or expect an X week delivery of specific scope, they wanted to sign on vague requirements that they could change as the project went along while keeping the vendor under pressure to deliver whatever thing they eventually found out that they wanted.
All of the hand-wringing in the article about estimation misses the point entirely.